The present invention relates to the field of intraocular implants, and more precisely to the field of lenses that are implanted after cataract surgery consisting in removing the natural lens from the capsular bag through a central and anterior capsulotomy (capsulorexis) having a diameter of 5 millimeters (mm) to 6 mm. As a result, the posterior and equatorial portions of the capsular bag are preserved.
Replacing the natural lens with an implant has become an operation that is commonplace in the field of cataract surgery.
Until now, the implants used have not had the ability to restore any faculty of accommodation to an operated patient. It is known that the loss of accommodation which leads to presbyopia stems not from loss of function in the ciliary muscle and the associated zonular fibers, but firstly from a hardening of the lens material contained in the capsular bag, and secondly from an increase in the dimensions of the lens due to the patient aging. Hardening of the lens material opposes any modification being made to its shape by the capsular bag when the capsular bag is relaxed by the zonular fibers (near vision). The increase in the size of the lens has the consequence that only a fraction of the amplitude in the variation of the dimension of the ciliary muscle is transmitted to the capsular bag, since during muscle relaxation, a portion of this amplitude is used up in tensioning the zonular fibers before beginning to cause the outward displacement that generates a modification in the shape of the lens.
With a young subject, the lens material on its own, i.e. when not enclosed in the capsular bag, has approximately the shape taken up by the lens when in the de-accommodated state (far vision). This is the state in which the lens material tends to harden with age. Still with a young subject, the rest shape of the lens, i.e. of the lens material in the capsular bag and in the absence of any connection with the zonular fibers, is close to that of the accommodated state (near vision). In other words, the elasticity of the capsular bag constrains the lens material to leave its own rest state and take up an accommodated shape. Hardening opposes this molding of the lens material by the capsular bag.
Likewise, with a young subject and in the accommodated state of the eye, the axial zonular fibers are always tensioned without slack. This enables them to transmit the amplitude of ciliary muscle deformation to the capsular bag in full. The increase in the size of the lens causes the axial zonular fibers to be relaxed when the ciliary muscle is contracted, so relaxation of the muscle has an effect on the capsular bag only over a fraction of its stroke, with the first portion of this increase in diameter having the sole effect of retensioning the axial zonular fibers so as to cause them to take up a position in which they are able to drive the capsular bag over a second portion of the increase in diameter of the ciliary muscle.
Thus, when cataract surgery fully conserves both the posterior portion of the capsular bag and its equatorial portion, and leaves a peripheral fraction of its anterior wall in place as well, the conditions are such that accommodation is capable of being recovered. The full capacity of the capsular bag for elastic deformation is recovered; in the absence of any lens material, the bag shrinks elastically and the zonular fibers are again under tension. It is then possible to take advantage of the still-functioning xe2x80x9cdrive assemblyxe2x80x9d constituted by the ciliary muscle, the zonular fibers, and the remaining portions of the capsular bag.
Numerous implants have been designed that attempt to make use of contraction and relaxation of the ciliary muscle in order to modify the optical power of the eye. Implants are known comprising two pieces, a case received in the capsular bag and an optical portion inside the case. The case is supposed to track the shape of the capsular bag. As a result, at least in theory, the optical piece is caused to move along the optical axis of the eye, thus varying the optical power of the eye and thus providing vision accommodation. In this respect, mention can be made of document EP 0 337 390. It would appear that that implant provides poor performance since the mechanism for compressing the case produces only a very small amount of movement in the optical portion, so the faculty of accommodation is practically non-existent.
One-piece implants are also known comprising an optical central portion and a haptic portion (e.g. two radial arms extending from the periphery of the optical portion) having the function of being held captive in the collapsed equatorial zone of the capsular bag and by the formation of fibrosis. After the implant has been put into place between the collapsed membrane portions, the operating method then consists in maintaining the ciliary muscle in the relaxed state for the time required (a few weeks) to allow fibrosis to take hold of the ends of the haptic portions. During this time, the remainder of the anterior portion of the capsular bag shrinks, thus tending to stress the haptic portions towards the posterior portion of the bag and thus to press the optical portion against this posterior portion. At the end of fibrosis growth, the ciliary muscle is returned to normal control by the brain. Thus, when it contracts for near vision, the capsular bag is released, and the fibrosis zone tends firstly to tilt forwards with help from an increase in the internal pressure of the eye, and secondly to tighten radially, thereby causing the optical portion to move forwards, the radial shrinkage being transformed by the hinged or flexible haptic arms into a movement tending to cause the optical portion to protrude forwards. To accomplish this movement and the opposite movement when the ciliary muscle relaxes, the haptic portions are hinged to the edge of the optical portion or they are very flexible so as to be capable of moving or bending in front of and behind the mean plane thereof, in front for far vision and behind for near vision. In addition, the haptic portions slide in their sockets in the fibrosis tissue which has been generated between the collapsed portions of the capsular bag in the vicinity of its equator. That type of implant is described in document U.S. Pat. No. 5,674,282, for example.
In that device, the fibrosis tissue whose growth is encouraged is a factor which contributes to modifying interaction between the zonular fibers and the capsular bag and which makes it impossible to predict the final behavior of the implant during accommodation.
Finally, proposals have been made for another one-piece accommodating implant comprising an annular portion whose section is gutter-shaped and intended for being received in the equatorial zone of the capsular bag and from which there project arms connecting it to a central optical portion. Variation in the diameter of the equatorial zone of the bag towards and away from the center gives rise to radial thrust or traction on the arms, thereby causing the optical portion to move along the optical axis (see WO 99/03427).
In that device, the presence of the continuous outer annular portion constitutes a brake on deformation of the equatorial zone of the bag, and that diminishes the effectiveness of the implant in providing accommodation.
Unlike known devices, the present invention makes it possible to retain as much as possible of the accommodation faculties still available in an eye that has been subjected to a cataract operation.
A first object of the present invention is to provide a one-piece implant, and a second object is to provide an artificial lens device which comprises the implant and an intermediate piece between the implant and the capsular bag.
In the present description, the terms xe2x80x9canteriorxe2x80x9d and xe2x80x9cposteriorxe2x80x9d should be understood in their meanings as used in ophthalmology, i.e. so far as the lens system is concerned, xe2x80x9canteriorxe2x80x9d is closer to the cornea, and xe2x80x9cposteriorxe2x80x9d is further from the cornea. In the description below, these two adjectives are used even for devices that have not been implanted, with the description being as though they were implanted.
Thus, the implant of the invention is an accommodating intraocular implant for locating in the capsular bag, the implant comprising a single piece of elastically deformable material constituting a central lens and at least two haptic portions in the form of radial arms for bearing via their free ends against the equatorial zone of the capsular bag; the free end of each radial arm is fitted with a shoe of substantially toroidal outside surface enabling the implant to bear against the equatorial zone of the bag, the connection between each shoe and the corresponding arm being of the hinge type situated in the vicinity of the posterior edge of the shoe and being formed by a first thin portion of the arm, while the connection between each arm and the lens is of the hinge type implemented at the anterior surface of the lens by a second likewise thin portion of the arm, the plane containing the first thin portions being situated behind the plane containing the second thin portions.
Several advantages result from this structure. Firstly, any movement tending to bring the shoes towards the center of the lens causes the lens to move forwards, which corresponds to contraction of the ciliary muscle for near vision.
This forward movement is made that much more meaningful when:
the shoes transmit the reduction in capsular bag diameter in full, unlike an equatorial ring which always provides a certain amount of resistance to radial contraction that needs to be overcome; and
the shoes reduce considerably the production of fibrosis tissue which would otherwise form a mass at the equator of the capsular bag that modifies the characteristics of the bag (towards less deformability), and thus its ability to respond over the greatest possible amplitude to variations in the tension of the zonular fibers. In this respect, it is preferable for the shoes to be quite long circumferentially, specifically for the purpose of opposing fibrosis growth (at least one-third of the circumference of the bag).
Preferably, the arms possess respective posterior projections so that in the most radially relaxed state, these projections bear against the posterior wall of the capsular bag and prevent the hinge planes from inverting, since that would prevent any accommodation.
Also preferably, each arm is in the form of an arch with the foot of each arch being connected to the lens via a thinned portion. It will be understood that by means of this shape, the working length of each haptic arm can be lengthened, and thus for given radial contraction greater amplitude can be obtained in the forward movement of the lens. The arm of maximum possible working length is an arm which is hinged to the lens at the ends of a diameter which extends perpendicularly to the middle radius of the arm. However, under such conditions the connection between the arm and the lens would be concentrated at the two ends of said diameter and that would make the orientation of the lens unstable. That is why a preferred embodiment is in the form of an implant having three haptic arms distributed at 120xc2x0 intervals around the lens.
In this respect, it should be observed that in order to obtain maximum movement of the lens, it is necessary to ensure that the gap between the anterior and posterior planes containing the two types of hinge is as small as possible in order to take advantage of the region of maximum variation in the sinewave function which governs the transmission of these movements.
Furthermore, the implant of the invention advantageously includes, between pairs of haptic arms, rigid radial extensions rooted in the periphery of the lens and forming abutments opposing expulsion of the implant from the capsular bag by coming into contact with the remaining portion of the anterior wall of the bag around the central opening that has been made therein. These extensions are located outside the bisectors of the angles between pairs of haptic arms so that the implant remains easy to fold along certain diameters thereof which have neither arms nor extensions.
When the arms are in the form of arches, the hinge connection between the lens and each foot of an arm takes place via these radial extensions, just outside the maximum diameter of the lens.
The invention also provides an artificial lens device which comprises, in addition to the above-described implant, an intermediate element that is elastically deformable, in particular in the radial direction, and that is designed to cover the interior face of the capsular bag or at least the equatorial zone thereof. Thus, in addition to the implant, the device also comprises an element which is separate from the implant, and which is elastically deformable, with at least a peripheral portion in the form of a radially deformable gutter whose diameter at the bottom of the gutter, in the rest state, is less than the outside diameter of the implant, as measured on the outside face of each shoe when in the rest state.
The outer equatorial diameter of the intermediate element, while in its rest state, corresponds to the equatorial diameter that the accommodated lens used to have when the intended subject was 20 to 30 years old.
When the implant is put into place in the gutter, an equilibrium state is obtained for the assembly which is such that the outer equatorial diameter of the assembly is greater than that of the intermediate element on its own and such that the equatorial diameter of the implant is less than that which it has at rest. This equilibrium state is the state reached when the radial contraction forces of the gutter-shaped piece are equal to the radial expansion forces of the implant.
By computer-assisted design methods, it is possible with given mechanical characteristics (i.e. given materials) to determine the various critical dimensions and shapes for the implant and for the gutter, particularly concerning the hinges of the haptic arms of the implant and concerning the thickness of the equatorial portion of the gutter, which together condition such or such an equilibrium state and the amount of energy required to modify it. It is then possible to match the implant to the subject who receives it, thereby optimizing the ability of the subject to accommodate.
For example, if the capsulorexis of the anterior wall is small in size and if the amount of fibrosis tissue produced by the subject is assumed to be small, then a device should be put into place in the capsular bag for which the equilibrium state is close to the accommodated state which the subject""s natural lens used to have when the subject was 25 or 30 years old. However, with capsulorexis of larger size and a tendency towards a large amount of fibrosis, the device to be put into place should have a rest state in which the implant takes up a position relative to the intermediate element that is close to far vision, with the outside dimension of the device still being that which the natural lens used to have in the de-accommodated state (in the absence of accommodation) when the subject was 25 to 30 years old.
After the device has been put into place in the capsular bag, the bag tends to contract elastically so as to come into contact with the element of the device which forms the case of the implant. Since the size of the case corresponds to the size the lens material used to have when the patient was young (25 to 30 years old), i.e. an age when the ability to accommodate is large, all of the components driving accommodation (and in particular the zonular fibers) are restored to their state of maximum efficiency as it existed at that time.